Radioreceiver



Jan. 2, 1934.

F. H. DRAKE 1,942,327

RADIORECEIVER Filed June 24, 1953 2 sheets-sheet 1 Jan. 2, 1934. F. H. DRAKE 1,942,327

RADIORECEIVER Filed June 24, 1933 2 Sheets-Sheet 2 Patented Jan. 2, 1934 RADIORECEIVER Frederick H. Drake, Boonton Township, Morris County, N. J., assignor to Aircraft Radio Corporation, Boonton, N. J., a corporation of New Jersey Application June 24, 1933. Serial No. 677,514

7 Claims.

This invention relates to radio receivers, and particularly to receivers in which the control of sensitivity may be shifted at will from manual to automatic.

An object of the invention is to provide means vfor quickly and easily selecting the type of reception best adapted for a given purpose. Another object is to provide means for adjusting either the radio or audio sensitivity of a radio lreceiver; and a further object is to provide convenient means for tuning a radio receiver of the type described by the use of the sense of hearing alone. More specifically, an object is to provide a radio receiver including a switching system ,for alternatively selecting either a manual or an vautomatic gain control, and a manual control of output level for use when the receiver gain is controlled-automatically; the two manual controls being adjustable by a single control member.

These and other objects and advantages of the invention will be apparent from the following specification, when taken with the accompanying drawingsin which:

Fig. 1 is a schematic 'diagram illustrating the general relationship of the several elements of a receiver embodying the invention;

Fig. 2 is a fragmentary circuit diagram of one embodiment of the invention;

Figs. 3 and 4 are simplified schematic diagrams showing only those elements of the Fig. 1 circuit which complete the manual gain control system and the automatic gain control with manual output level control system, respectively; and

`Fig. 5 is a view of a remotely-controlled receiving system in which the invention is incorporated.

The invention is particularly useful in the case of aircraft or automobile receivers as any simplification of the control facilitates operation of the receiver by the pilot or driver and the invention will be described as incorporated in an airplane receiver but it is to be understood that the invention is not restricted to this particular use. Automatic vgain control receivers are intended to simplify operation and to provide better tone qualitybyl eliminating overloading, but the accurate tuning of this type of receiver is rendered difi'icult by the fact that the audio output level may vary but slightly over a substantial range of adjustment of the tuning controls. Tuning meters have been included in the receiver to indicate an adjustment of the tuning control to resonance at a desired frequency but tuning by observation of a meter is inconvenient', particularly when the operator is simultaneously con- (Cl. Z50-20) trolling an airplane or automobile. Most receivers of the automatic gain control type include a manual adjustment of the audio level at the output device, which device may be a telephone receiver, a loud speaker, an indicator or the like. As shown schematically in Fig. 1, a receiver embodying the invention includes the usual ele.-` ments, such as a radio frequency amplifier 1 of the type having one or more tubes .for amplifying the received carrier wave at the received frequency and/or at a beat frequency, a detectorv and audio amplifier 2 and an output device 3. The control system includes a manual sensitivity control 5, an automatic gain control 6 and a manual output level or audio sensitivity con` trol 7; the several controls being associated with the receiver circuits by switches 8, 9, 9 that are ganged for actuation by a single adjustable element, such as knob l0. As shown in Fig. 1, the', knob 10 isadjusted to close switch 8, thus throwing the receiver over to manual sensitivity control, and to open switches 9, 9' of the automatic gain control 6 and output level control 7.

The advantage of. such a control system is that meter` tuning to resonance is eliminated since the receiver may be accurately tuned when set for manual sensitivity control, and the operator may i then shift to automatic gain control with the assurance that signals willbe received with maximum fidelity and, in the case of ,an aircraft receiver, at a maximum distance from the'` transmitter. f

As shown in Fig. 2, the radio amplifier l may A include a pair of tubes 11 which are cascaded by y suitable coupling means, not shown, and to which the signal energy received at an. antennafA is transferred through ran input circuit 12 which preferably includes a tuning element. The cletector 13 of the audio unit 2 is coupled to the radio amplifier 1 by a tuned circuitY 14 which, when the amplifier 1 does not include a frequency changer, is preferably tuned to the desired carrier frequency by an adjustable `element that is mechanically connected to the adjustable element of the tuned input circuit 12, as indicated graphi cally by the broken line- The detector is illustrated asa diode having an output resistance 16V across which both audio frequency and directl current voltages are developed, the audio component being impressed on the amplifier tube 17,

19, the resistance 18 cooperating with the radio frequency bypass condenser 20 shunting outputr resistance 16 to form a filter. rent voltage developed across resistance 16 may through a resistance 18 and blocking condenser The direct curllO be returned to one or more of the radio amplifier tubes 11 as a gain control voltage, the biasing circuit including a low pass filter, comprising resistance 21 and condenser 22, and decoupling resistances 23 in series with the individual control grids G1 when the automatic control is applied to more than one ampliiier tube. A lead 24 extends from the grid terminal of the filter resistance 21 to one of the stationary spring contacts 25 of a switch, the second contact being grounded and the switch being closed when the insulating disk 26 is rotated to carry the pin 27 into engagement with the contacts 25. Y

A second biasing means is provided for the controlled tube or tubes 11 by cathode bias resistances 28 which are connected by a lead 2S to the sliding contact 29 on a manual gain control resistance 30, and to one contact 3l of a grounding switch which has a contact pin 32 mounted on the disk 26. When the grounding switch is open, as illustrated., the cathode circuit is completed to ground through resistance and a series resistance 33.

The output device 3 is connected between ground and the high potential terminal of the transformer 34, the primary of the transformer being included in the plate circuit of the audio Mamplier tube 17. The high potential terminal of the output device 3 is also connected by lead 34 to the sliding contact 35 on an audio level control resistance 36 which is connected, by lead 37, to one of the contacts 38 of a grounding switch, the contact pin 39 of the switch being mounted on the disk 26.

The disk 26 also carries a pair of contact pins 40 at opposite sides of the stationary contacts 41, thus providing a switch for closing the power supply circuits tothe receiver when the disk is I rotated in either direction from its illustrated position. y Y

As shown diagrammatically, the contacts 41 are included in a connection 42 between a source r of cathode heater current, indicated by the legend -l- A and the heaters Hf The disk 26 is provided with indexing notches 43 for cooperation With a spring latch 44 and carries a pointer 45 Vwhich alines radially with one of the legends Manual, Oi and Auto, to indicate the effective position of the gang switching disk 26.

The sliding contacts 29 and 35 on the resistances 30, 36, respectively, are adjusted simultaneously by a common operating member 46. As indicated by the arrow and the accompanying legend Increase, the resistances 30, 36 are so connected in their associated circuits that an adjustment of the operating member 46 in the indicated direction will result inan increased output at the phones 3 whether the gang switch be set for manual sensitivity control or for automatic gain control with manual adjustment of the output level.

As illustrated in Fig. 2, the pointer 45 is alined with theA legend rOff and indicates that the receiver is not in operation. When the disk`26 is rotated counterclockwise to aline the pointer with the legend Manual, the power supply circuit is closed and contacts 25, 27 are engaged, the other groundingA switches being opened. The switch 25, 27 grounds the decoupling resistances 23 and thereby renders the automatic gain control system inoperative while the open switch 3l, 32'renders the manual output level control inoperative. The operative elements of the control resistances 28, 30 and 33 in the cathode circuit of one or more of the radio amplifier tubes, the effective value of the resistance 30 being adjustable manually by means of the sliding contact 29 to control the receiver sensitivity and the audio output level. 1

For automatic gain control, the gang switching disk 26 is rotated clockwise to aline pointer 45 with the legend Auto, thus closing the power circuit at contacts 41, 42; opening contacts 25, 27 to render the automatic gain control operative; closing contacts 31, 32 to short out the resistances 30, 33 of the cathode circuits of the controlled tubes; and closing contacts 38, 39

'torender the manual output level control operative. The essential elements of the control system` thus established are shown in Fig. 4.

As illustrated diagrammatically, the resistances 30,36 are preferably tapered, in accordance with known design principles, to provide a desired relationship between signal attenuation and the displacement of the common control member 46. The xed resistances 28 in the cathode circuits provide the appropriate bias when resistances 30, 33 are'shorted out during automatic gain control operation; and the resistance 33 is so chosen as to equalize the audio output in the telephones 3 at a chosen power output level vwhen the control member 46 is positioned for maximum gain on manual sensitivity control, i. e., with this setting of the control member 46, the chosen output level is the same whether the gang switches be adjusted to manual or to automatic gain control position. The signicance of this equalizing resistance is that an aircraft pilot who has tuned in a weak signal by setting the switches for manual sensitivity con-V trol can'then shift to automatic gain control with the knowledge that, so long as the signal is of such strength as to be readable by manual adjustment of sensitivity, it will be received on the automatic gain control setting. VThe pilot therefore has no occasion to devote his attentions to a manual control in the' expectation that better results may be obtainedby Athat type of control.

In general, however, the receiver on aircraft is tuned to a transmitter at or near the iiying field at the start of a flight and, by use of the manual sensitivity control, the receiver mayv be readily tuned to exact resonance with the signal frequency. The switches are then thrown to' yetc.. The radio receiver 4'7, including the amplier circuits `and tubes, comprises a unit which may be mounted in the fuselage aft of the pilots seat-and tuned by artuning unit 48, on the instrument panel, the units being connected by aiiexible shaft housed inV a protective cover 49. The receiverY is connected to the antenna struc- 'ture by a lead .50 and is grounded on the fuselage by a connection 51.y The various circuit connections to the receiver arey made by a cable 52 which runs to a junction box 53 that is usually mounted adjacent'the customary ignition battery 54, and preferably at the rewall back lil() a cable 57 extends from the junction box to a single small box 58 which houses all of the described control elements and which is to bemounted in a readily accessible position inside the cockpit, usually near the throttle controls of the plane, thus permitting the pilot to make the necessary adjustments with the hand which also operates the throttle. A pair of telephones 3 suitable for inclusion in the pilots helmet are plugged into a jack in the control box 58, and the handle constitutes both pointer and the means for adjusting the switch disk 26 to the desired position. The legends Man (as an abbreviation of manual), Off and Auto appear on the face of the box 58 in the relative positions shown in the circuit diagram, Fig. 2. The adjustable control resistances are of the rotary contact type, with contact arms mounted on a common shaft which carries an adjusting knob 46', an arrow being engraved upon the knob to indicate the direction of rotation for an increase in the output level.

In operating the receiver, the airplane pilot throws handle 45' to the Man position with knob 46 advanced suitably. He tunes the receiver to resonance with the desired signal by means of a remote mechanical tuning control 48, resonance being indicated by a maximum signal output in the telephone receivers 3. The use of a visual tuning meter would be highly undesirable for many reasons, among which are the necessity for concentration of the sense of sight upon the operation of the airplane, particularly in formation flying. As soon as the signal is tuned in, the pilot switches to Auto and adjusts the output level to a suitable value, depending upon his own aural acuteness, by means of knob 46'. The amplifier gain is thenceforth varied automatically by the automatic gain control system.

The simple and rapid change from an automatic to a manual sensitivity control permits the pilot to interrupt the reception of signals from his home station or other transmitter to listen intermittently to guiding signals from a radio range beacon, the beacon signals now commonly employed being of a type which cannot be successfully received with automatic gain control.

The novel control system may be incorporated in receivers of widely different types of physical construction and electrical design. For example, the adjustable resistances 30, 36 of the radio sensitivity control and the audio transmission control, respectively, may be included in other types of control circuits, such as the voltage divider type commonly employed for regulating either radio or audio sensitivity.

I claim:

1. In a radio receiver, the combination with a radio frequency amplifier, a detector, an audio amplier, and an output device, of adjustable means for controlling the sensitivity of said radio amplifier, adjustable means for controlling the ratio of the output level at said output device to the radio input at said detector, switch means adjustable to alternative positions to render either of said adjustable means operative and the other inoperative, and a manually-operated control ymember for simultaneously adjusting both of said 'adjustable means.

2. In a radioV receiver, the combinationfwith a radio frequency amplifier, -a detector, an audio amplifier, and an output device, of adjustable means for controlling the sensitivity-of said radio amplifier, adjustable means for controlling the ratio of the output level at said output device to the radio input at said detector, switch meansA adjustable to alternative positions to render either of said adjustable means operative and the other inoperative, and a manually-operated control means for simultaneously adjusting both of said adjustable means to produce a change of output level in the same sense whether said switch means be adjusted to one or the other of its alternative positions.

3. A radio receiver as claimed in claim 1, in combination with means for automatically ycontrolling the gain of said radio frequency amplier to maintain the radio input to said detector substantially independent of variations in the strength of the received carrier wave, and wherein said switch means includes means rendering said automatic gain control means operative only when said switch is adjusted to that position which renders said adjustable sensitivity control means inoperative.

4. In a radio receiver, the combination with a radio frequency amplifier, a detector, and an output device; of manual sensitivity control means including a manually adjustable resistance for determining the gain of said amplifier, automatic control means including means automatically biasing said amplifier to render the radio input to said detector approximately constant over a wide range of received signal strength and a manually adjustable resistance for determining the audio level at said output device, switch means adjustable to connect either of said control means in circuit while simultaneously rendering the other control means inoperative, and a common control member for simultaneously adjusting both of said adjustable resistances.

5. In a radio receiver, the combination with a radio frequency amplifier, a detector, and an output device; of manual sensitivity control means including a manually adjustable resistance for determining the gain of said amplifier, automatic control means including means automatically biasing said amplifier to render the radio input to said detector approximately constant over a wide range of received signal strength and a manually adjustable resistance for determining the audio level at said output device, switch means adjustable to connect either of said control means in circuit while simultaneously rendering the other control means inoperative, and control means for simultaneously adjusting both of said adjustable resistances to produce a variation of output level in the same sense irrespective of the adjustment of said switch means.

6. In a radio receiver, the combination with a radio frequency amplifier, a detector, an audio frequency amplier, an output device, means for automatically controlling the gain of said radio frequency amplifier, and means including a manually adjustable resistance for controlling audio transmission through said receiver, of means including a manually adjustable resistance for controlling the sensitivity of said radio frequency amplier, switch means adjustable to one position to render said gain control and said audio transmission control means operativewhile ren-V dering said sensitivity-control means inoperative and adjustable to a second position to render said gain control and said audio transmission control means inoperative while rendering said sensitivity control means operative, a common Y operating member for simultaneously adjusting both of said adjustable resistances to produce an output level-variation in the same sense irrespective of theA position of said switch, and means for equalizing the audio output level at a predetermined value when said operating member is positioned to adjust said resistances formaximum sensitivity, :whereby the chosen output level is the same at saidadjustment position irrespec` 

